Re: Bypassing NULL elements in row_to_json function

On 04/10/2016 09:24 AM, David G. Johnston wrote:
> On Sun, Apr 10, 2016 at 8:39 AM, Michael Nolan <htfoot(at)gmail(dot)com
> <mailto:htfoot(at)gmail(dot)com>>wrote:
>
> Here's what I did:
>
> \d gold1604_test
> Table "uscf.gold1604_test"
> Column | Type | Modifiers
> --------+------+-----------
> data | json |
>
> Some sample data:
> {"id":"10000001","name":"MISNER, J
> NATHAN","st":"NY","exp":"2012-05-31","sts":
> "A"} +
>
> {"id":"10000002","name":"MISNER,
> JUDY","st":"TN","exp":"2007-07-31","sts":"I"}
> +
>
> {"id":"10000003","name":"MISNER, J
> AMSCHEL","st":"NY","exp":"2007-05-31","sts"
> :"A"}+
>
>
> ​(I think) PostgreSQL assumes that there is only a single top-level json
> element, whether it be an array or an object. The first thing you'd
> have to do is split on the newline and create a PostgreSQL text array.
>
>
> But,
> uscf=> insert into goldmast_test select * from
> json_populate_record(NULL::"goldmast_test", (select * from
> gold1604_test limit 2) )
> uscf-> \g
> ERROR: more than one row returned by a subquery used as an expression
>
> Is there a way to get around the one row per subquery issue?
>
>
> ​Yes, use LATERAL.
>
> Something like the following should work (not tested):
>
> INSERT INTO goldmast_test
> SELECT jpr.*
> FROM gold1604_test
> LATERAL json_populate_record(null::goldmast_test", data) AS jpr

I can confirm this works after a little clean up:

test=> INSERT INTO goldmast_test
SELECT jpr.*
FROM gold1604_test,
LATERAL json_populate_record(null::"goldmast_test", data) AS jpr;
INSERT 0 3

test=> select * from goldmast_test ;
id | name | st | exp | sts | supp | rrtg |
qrtg | brtg | oqrtg | obrtg | fid
----------+-------------------+----+------------+-----+------+------+------+------+-------+-------+-----
10000001 | MISNER, J NATHAN | NY | 2012-05-31 | A | | |
| | | |
10000002 | MISNER, JUDY | TN | 2007-07-31 | I | | |
| | | |
10000003 | MISNER, J AMSCHEL | NY | 2007-05-31 | A | | |
| | | |
(3 rows)

While trying to figure out how it works I discovered the LATERAL is not
necessary:

test=> INSERT INTO goldmast_test
SELECT jpr.*
FROM gold1604_test,
json_populate_record(null::"goldmast_test", data) AS jpr;
INSERT 0 3

test=> select * from goldmast_test ;
id | name | st | exp | sts | supp | rrtg |
qrtg | brtg | oqrtg | obrtg | fid
----------+-------------------+----+------------+-----+------+------+------+------+-------+-------+-----
10000001 | MISNER, J NATHAN | NY | 2012-05-31 | A | | |
| | | |
10000002 | MISNER, JUDY | TN | 2007-07-31 | I | | |
| | | |
10000003 | MISNER, J AMSCHEL | NY | 2007-05-31 | A | | |
| | | |
10000001 | MISNER, J NATHAN | NY | 2012-05-31 | A | | |
| | | |
10000002 | MISNER, JUDY | TN | 2007-07-31 | I | | |
| | | |
10000003 | MISNER, J AMSCHEL | NY | 2007-05-31 | A | | |
| | | |
(6 rows)

>
> ideally you could just do (not tested):
>
> INSERT INTO goldmast_test
> SELECT jpr.*
> FROM (SELECT t::json FROM unnest(string_to_array(?::text, E'\n') un
> (t))) src j
> LATERAL json_populate_record(null::goldmast_test", j) AS jpr
>
> Where the "?::text" is placeholder for the textual JSON being handed to
> the query thus avoiding the temporary "gold1604_test" table.
>
> David J.
>

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com